The goal of this proposal is to evaluate a new approach for nanotherapy of lymph node metastatic breast cancer. Imaging-capable nanodrugs, which distribute to tumors and the lymphatics will be designed to carry locked-nucleic acid (LNA) knockdown probes targeting microRNA-10b (miR-10b), known to mediate tumor invasion and migration of breast cancer cells and miR-21, implicated in tumor cell proliferation and survival. In our preliminary studies, we have demonstrated the feasibility of the proposed method. We have shown that treatment of invasive breast tumor cells with the miR-10b-targeted nanodrug results in an 88% downregulation of miRNA-10b with the application of just 1.5 nmoles/ml of LNA and abolishes the invasion and migration of the tumor cells. In vivo, we have obtained results suggesting that after intravenous delivery to tumor-bearing mice, a tumor-targeted version of the nanodrug leads to robust tumor uptake detectable by in vivo imaging and, importantly, results in elimination of bioluminescence imaging-detectable tumor cell metastasis from the primary tumor to lymph nodes. If treatment is initiated after the appearance of lymph node metastases, the nanodrug arrests the metastatic process. These earlier findings form the basis for the current application, in which we propose to extend these studies in order to mediate long-term prevention, arrest, and regression of metastases. This will be accomplished by concurrently targeting the pro-metastatic miR10b and the pro-proliferative and anti-apoptotic miR-21. Combination treatment with chemotherapy will also be explored. The delivery will be coupled with the concurrent non-invasive imaging of the delivery process. We will evaluate changes in metastatic burden and will compare our imaging conclusions to ex vivo studies.